1. Field of the Invention
The present invention relates to a DC offset canceling control method which obtains a DC offset value generated in a transmitter/receiver, holds the obtained DC offset value therein, and removes it from received data, and a transmitter/receiver using the same method.
2. Description of the Related Art
A receiver that receives data has conventionally included a DC offset cancel circuit. The DC offset cancel circuit removes a DC offset value that has got mixed in with received data at each part in the receiver to reduce an error rate of the received data. U.S. Pat. No. 6,639,909 (document 1), for example, describes a receiver including such a DC offset cancel circuit.
The receiver described in the document 1 receives a signal of time division multiple access (TDMA) system.
Then, the DC offset cancel circuit turns off a power supply of a mixer within a guard time period between transmitted and received bursts, obtains a DC offset value generated in the receiver located at the post stage of the mixer, and holds the obtained value. During a period of detecting the DC offset value, the transmitter/receiver can neither transmit nor receive data. The DC offset cancel circuit subtracts the held value from the received data.
However, the technology described in the document 1, which is related to a receiver for receiving a signal of time division multiple access (TDMA) system, cannot directly be applied to a transmitter/receiver in a packet switching system, which uses CSMA/CA (carrier sense multiple access with collision avoidance).
The receiver receiving a TDMA based signal detects a guard time period between transmitted and received bursts on the basis of a frame synchronization signal contained in the received signal.
However, in the packet switching system for transmitting and receiving a CSMA/CA based signal, a transmitter/receiver checks (carrier sense) a carrier usage prior to data transmission. When the carrier is not in use (idle), the transmitter/receiver transmits data according to a priority level of each data in a data group to be transmitted. When the carrier is in use (busy), the transmitter/receiver postpones data transmission till the carrier becomes idle. In other words, since the CSMA/CA based signal does not contain the frame synchronizing signal, the transmitter/receiver based on CSMA/CA system cannot detect a time period corresponding to the guard time period of TDMA system.